Effect of exercise intensity on the spectral properties of skin blood flow

The effect of exercise intensity on the power spectral properties of the periodic oscillation of the skin blood flow was investigated with respect to the variability of heart rate in 7 healthy male subjects. The skin blood flow (SBF) and heart rate (HR) were measured by a laser-Doppler flowmeter on the forehead skin, and by an ECG, at rest and during bicycle exercise in three different intensities; unloaded, 50 and 100 W. An alcohol ingestion test was additionally performed on two subjects in the resting condition. Power spectral density (PSD) was calculated by means of fast Fourier transform (FFT). The peak frequency (PF) and integration of PSD (iPSD) of each component was estimated to compare conditions and parameters. In the SBF fluctuation, two major components were usually observed: one synchronous with cardiac contraction rhythm (HFF) which shifted to a higher frequency band with exercise; the other was located in a lower frequency band (LFF) ranging from about 0.1 to 0.2 Hz and did not shift with exercise. The PF of the LFF in the SBF was significantly different from that of the HR, called Mayer waves. The iPSD of the LFF in the SBF increased with increasing intensity of exercise but finally decreased at the highest intensity for which the HFF exhibited a marked increase. The LFF in the SBF disappeared after oral ingestion of alcohol that induced an increase of the SBF. From these spectral analyses, it is proposed that the LFF in the SBF is mainly related to the vasoconstrictor activity through the skin sympathetic pathway, and that the intensity of exercise does not modulate the periodicity of this fluctuation.